1. Field of Invention
The present invention relates to a method for varying speech speed, and more particularly to a method based on pitch period of speech signal to vary the speech speed.
2. Related Art
For the electronic apparatuses equipped with language learning functions, language conversations intended to learn may be recorded in the apparatus in advance. The electronic apparatus may be portable to allow the user learning language wherever and whenever. However, every user is at different learning level; the same speed for playing a section of conversation may be proper to understand for some users, but too fast to understand for others. Therefore, a so-called speed-varying function becomes one of the major functions of the language-learning apparatus.
Speed variation indicates that the language-learning apparatus varies the playing speed by user's demand while playing speech(s), accompanying with the same tone under various speeds. So ideally no matter the speed variation becomes slower or faster, users may all listen clearly; which is really helpful to language learning.
Although the conventional language-learning apparatus has the speed-varying function, usually the speech played through speed variation is distorted. Since the speech signal is a continuous analog signal, the voiceprint frequencies generated from different persons' pronunciations or different sound sources are different. A common speed-varying technology is to repeatedly play the sampling speech data, or to play intermittently by intervals, thereby facilitate the speed-varying function. Such approach will provide decelerated or accelerated playing speeds and the same signal envelope as the original speech. However, it also generates echoes and machine noises, leading to decreases of the voiceprint frequency; the effects are just like decelerating or accelerating the rotation speed of a recorder motor, which causes obvious distortions.
Therefore, how to maintain the tone of the original speech without distortion while the user operates the speed-varying function on a language-learning apparatus has become an issue required to be urgently solved.